The present application is based on Japanese patent application No. H11-50958 filed on Feb. 26, 1999, the entire content of which is hereby incorporated by reference.
The present invention relates to a hexaaryl biimidazole (HABI) compound useful as a photopolymerization initiator, a photosensitive composition containing the compound, a method of manufacturing patterns made of the compound, and electronic components incorporating such patterns.
Photosensitive resin compositions have been used in a wide range of industrial applications such as UV inks, print screens, most recently laser holograms, and the like. Photosensitive heat resistant polymers serve not only as positive-type photoresists that make miniaturization of semiconductors possible, but also as protective coating or negative buffer coating, and as passivation film. One example of such photosensitive heat resistant material is disclosed in Japanese examined patent publications Kokoku H5-67026 and Kokoku S63-3139, which teach the reaction of an aromatic diamine compound with an aromatic tetracarboxylic dianhydride to yield a photosensitive group.
A reduced-size projection-type exposure apparatus called xe2x80x9cstepperxe2x80x9d is used for forming patterns in a semiconductor production line. The g-line stepper (using visible light of 435 nm wavelength generated by an ultra high-pressure mercury lamp) was commonly used previously. However, it is being replaced by the i-line stepper (using light of 365 nm wavelength) which meets the more stringent miniaturization design rules adopted in the manufacture of semiconductor devices.
Photosensitive polyimide precursors which have aromatic monomers as their skeleton provide excellent heat resistance and mechanical properties as photoresists. However, such polyimide precursors themselves absorb light. Their transmittance is low in the UV band, and particularly low in the i-line band (365 nm wavelength). The photochemical reaction in the exposed region of a layer of polyimide precursor is so small that it results in little sensitivity, thereby causing deterioration of the pattern shape obtained with the photoresist.
With the emergence of the Lead on Chip (LOC) technology, which is a high density packaging technique for semiconductor elements in which even thicker polyimide films are used, the low transmittance of polyimide precursors has become a serious problem in the lithography of semiconductor devices. Currently in demand in the market is a photosensitive polyimide having excellent sensitivity even at the bottom of the surface protective layers of semiconductor components, where the intensity of the i-line stepper is extremely reduced, therefore making possible the formation of patterns of excellent shape.
Among the components of a photosensitive resin composition, the photopolymerization initiator has the potential of having the greatest effect on the sensitivity. Commonly used photopolymerization initiators which are highly sensitive under the above described conditions include:
1. oxime ester compounds (e.g., 1-phenyl-1,2-propanedione-2-(o-ethoxy carbonyl)oxime); and
2. hexaaryl biimidazole compounds (e.g., 2,2xe2x80x2-bis(o-chlorophenyl)-4,4xe2x80x2,5,5xe2x80x2-tetraphenyl biimidazole (known as o-Cl-HABI)).
However, oxime ester compounds generally are not stable against heat, and separation of Cl ions has been a problem with chlorine-containing hexaaryl biimidazoles such as o-Cl-HABI in semiconductor processing. Neither of these initiators have brought satisfactory results as yet. In addition, o-Cl-HABI is poorly soluble in solvents so that the amount that can be used has not been sufficient for obtaining a good sensitivity.
The present invention provides a novel hexaaryl-biimidazole compound that has much better solubility and sensitivity than obtained with conventional technology, and therefore, can be used as a highly sensitive photopolymerization initiator.
The present invention also provides a photosensitive composition characterized by excellent photosensitivity and excellent pattern shaping under a low level of exposure to light.
In addition to resolving the above problems, the present invention provides a photosensitive composition containing a polyimide precursor that can form a polyimide film having excellent heat resistance and chemical resistance, and therefore, is suitable for forming a film for protecting the surface of semiconductor elements and forming interlevel dielectric films of thin layer multilevel printed circuit boards.
The present invention offers the following advantages:
the ability to form patterns having excellent photosensitivity and excellent pattern shape even under a low level of exposure;
the ability to develop the film into a pattern by reaction of the photosensitive composition with an aqueous alkali solution; and
the ability to manufacture patterns from polyimide which is a material with excellent heat resistance and chemical resistance.
Furthermore, the present invention provides electronic components having excellent reliability due to the characteristics of the above patterns.